Miniature potentiometer with friction wheel drive

ABSTRACT

A miniature rotary potentiometer having an arcuate resistance element and a rotary contact movable through less than one complete turn or revolution in brushing over the active extent of the resistance element. The rotary contact is mounted upon a rotatable carrier which also carries the pivots of a plurality of friction planet wheels the peripheries of which frictionally engage and travel along a circular path on the inner wall of the potentiometer housing and which peripheries are frictionally engaged by and driven by a small rotary spindle or hub carried by a tool-rotatable actuator disposed in the top or upper end of the potentiometer. Rotation of the actuator frictionally rotates the friction planet wheels which through their pivots drive the carrier at reduced rotary speed relative to the actuator, whereby the actuator must be rotated several complete revolutions to drive the contact along the extent of the resistance element.

D United States Patent 13,614,703

[72] Inventor Ronald L. Froebe 3,469,225 9/1969 Wood 338/163 21 1 pp No.git zg i Primary Examiner-Laramie E. Askin Assistant Examiner-Gerald P.Tolin [22] Filed Apr. 1,1970 F B P t 451 Patented Oct. 19,1971 e [73]Assignee Bourns, Inc.

ABSTRACT: A miniature rotary potentiometer having an arcuate resistanceelement and a rotary contact movable [54] MINIATURE POTENTIOMETER WITHFRICTION through less than one complete turn or revolution in brushingWHEEL DRIVE over the active extent of the resistance element. The rotary7 Claims, 8 Drawing Figs contact lS mounted upon a rotatable carrierwhich also carries the pivots of a plurality of friction planet wheelsthe periphe- [52] US. Cl 338/174, ries of which f i i ll engage andtravel along a circular 338/163 path on the inner wall of thepotentiometer housing and which [51] Int. Cl H0lc 9/02 peripheries arefrictionany engaged by and driven by a Small [50] Field Of Search..338/l62l64, :otary spindle hub carried by a too| rotatab1e actuator174 disposed in the top or upper end of the potentiometer. Rota-References Cited tion of the actuator frictionally rotates the frictionplanet wheels which through their pivots drive the carrier at reducedUNITED STATES PATENTS rotary speed relative to the actuator, whereby theactuator 3,355,693 I 1/1967 Van Benthuysen 338/164 X must be rotatedseveral complete revolutions to drive the con- 3,388.365 6/1968 Wood338/162 tact along the extent of the resistance element.

MINIATURE POTENTIOMETER WI'I'II FRICTION WHEEL DRIVE BRIEF SUMMARY OFTHE INVENTION a. The environment of the invention and the prior art.

In prior art potentiometric instruments of the type popularly calledsingle-tum adjustment or trimming potentiometers and which arecharacterized by an arcuate resistance element of slightly less than 360angular extent, a shaft or rotor is generally employed to carry amovable potential-adjusting contacting in an arcuate brushing or wipingpath along the surface of the resistance element. Stop means arecommonly provided for restricting movement of the contact off either endof the element. In the case of such potentiometers in the largesizerange (of the order of 1 inch diameter and larger), a shaft is providedon which a manually rotatable knob is secured, thus increasing theleverage that may be exerted in adjusting the contact and the precisionwith which adjustment may be made. In the case of medium-sizepotentiometers of the noted type (of the order of 55 inch to 1 inchdiameter), a contactcarrying rotor is generally employed, which rotorhas an end protruding from, or at least accessible from, the exterior orhousing of the potentiometer, the rotor having a slotted end forreception of a tool such as a screwdriver that is manually rotated toeflect potential-adjusting movement of the contact along the resistanceelement. That means of adjusting such medium-size adjustmentpotentiometers in many instances leaves something to be desired as tofineness or accuracy of adjustment easily accomplished; and as aconsequence, it has been previously proposed to interpose reductiongearing between the manually rotatable rotor and a member carrying therotary contact, whereby several turns or revolutions of the screwdriverand rotor are required to traverse the contact along its arcuate path ofless than 360". Such speedreducing" gear means have been found to befeasible, mechanically if not economically, in the larger models ofmedium-size single-tum adjustment potentiometers; but have been found tobe impractical in small-size potentiometers (less than 9% inch maximumdimension) because of lack of space for operable gears, weakness of gearteeth and gear spindles of the small sizes required, and allied reasons,such as excessive cost. It may be noted that the contact must berotatable through all of its prescribed path and from any positiontherealong to either end of the path as defined by stop means, but isgenerally prohibited from being moved beyond either end by the stopmeans. Thus gearing interposed between the manually driven actuator andthe contact carrier, although capable of transmitting the requiredtorque without damage other than normal wear, must survive relativelylarge torque overloads incident to arrest of the contact carrier by thestop means when the contact is driven to either extreme of its path andthe operator continues to apply torque to the actuator. Thus suchgearing, will in theory offering advantages of increasing value as thesize of the potentiometer is decreased, has been found to beeconomically impractical in miniature single-tum rotary potentiometers.

b. the present invention.

The invention disclosed hereinafter in detail is a miniature single-tumrotary potentiometer comprising a driving mechanism which provides allof the advantages of the noted reduction-gear or speed-reducing drivingmeans for the contact, without any of the disadvantages. The noveldriving mechanism is such that several turns or revolutions of themanually operated actuator are required for rotation of thepotential-adjusting contact through its entire traverse of theresistance element of somewhat less than 360 angular extent; and it issuch that continued application of torque and driving rotation to theactuator after arrest of contact rotation by the stop means ispermissible and does not result in any damage to the mechanism.Additionally, the expense of forming or cutting gears is avoided, andthe parts are easily and inexpensively produced and assembled, wherebythe potentiometer may be of very small size and is economicallypractical. The

reduction-gear or speed-reducing effect is attained in a simple andhighly effective way by forming the contact carrier as a planet carrierwith means for supporting or carrying in driving relation thereto a setof planet members of wheel form, each rotatable on its own axis on theplanet carrier and each having a rim frictionally engaging a circularpath on the interior wall of the potentiometer housing and each furtherfrictionally engaging a driving stub preferably formed as an axialextension of the manually driven actuator. Whereby the forces createdand involved are balanced, the planet members or wheels are preferablyuniformly spaced apart relative to the circular path or track. While theset of planet members may comprise three or four wheels, a setcomprising only two wheels has been found to operate with completesatisfaction. In all cases, each wheel contacts the circular path andthe driving stub of the actuator. Thus rotation of the small diameterdriving stub of the actuator causes rotation of the planet members abouttheir respective axes and consequent rotational travel of the planetmembers along the circular path engaged by their rims. The planetmembers thus partake of orbital motion around the axis of the stub; andsince they are supported by the rotatably supported carrier, the latteris also slowly rotated about that axis. The number of revolutions of theactuator and stub required to rotate the carrier and its contact throughthe full traverse of the resistance element is dependent upon therelationship between the diameters of the driving stub and the circularfriction path defined on the inner wall of the potentiometer housing,and may be, for example, four revolutions. Thus precision of adjustmentof the potentiometer, despite its very small dimensions, is excellent,and precise adjustment is easily accomplished. Further, when theactuator has driven the contact carrier to the point where motion of thecontact is arrested, continued rotation or overdriving" of the actuatormerely causes slipping of the planet member rim surfaces relative to thesurface of the driving stub, without any harmful or undesired effect.Following such overdriving, reverse rotation of the actuator isimmediately effective to reversely rotate or drive the carrier and thecontact. In a preferred embodiment of the invention, the planet membersare formed as wheels, each having an integral stub axle and pivot, and africtional rim. The carrier is, in the preferred form of the invention,formed as a rotary plate having recesses or nests and bearings providingguides for the respective planet wheels, each recess or nest being openadjacent the outer edge of the carrier to permit the frictional rim ofthe associated planet wheel to engage the arcuate friction path on theinner wall of the housing. The carrier is thus a dual-function member,carrying the electrical contact on one face and the planet wheels on theopposite face. The carrier is preferably constrained to rotate about theaxis of the driving stub by having a central bore or bearing in which anaxle on the lower end of the driving stub rotates, and/or by beingconfined at its circular periphery by suitably formed portions of theinner wall of the potentiometer housing. In the embodiments hereinillustrated, an extension of the driving stub forms a rotary gudgeon oraxle on which the contact carrier rotates.

The preceding brief description of the invention relative to the priorart indicates that it is a primary object of the invention to provideimprovements in miniature single-tum adjustment potentiometers.

It is another object of the invention to provide a miniature rotarypotentiometer having a simple and economical speedreduction rotarydriving mechanism.

Another object of the invention is to provide an improved drivingmechanism for a miniature single-tum rotary potentiometer.

Other objects and advantages of the present invention will hereinafterbe set out or made evident in the appended claims and the followingdescription of a presently preferred physical embodiment of theinvention as illustrated in the accompanying drawings.

THE DRAWINGS The presently preferred embodiments of the invention isillustrated in the accompanying drawings which are part of thisdescription or specification and in which drawings:

FIG. I is a pictorial view, grossly enlarged, of the miniaturesingle-tum adjustment potentiometer comprising the present invention;

FIG. 2 is a vertical cross-sectional view of the potentiometer depictedin FIG. 1, on a larger scale, showing the vertical arrangement of therotary operating components relative to the external shell or housing ofthe potentiometer, the sectioning being as indicated by directors 22 inFIG. 1;

FIG. 3 is a vertical cross-sectional view of the illustrative exemplarypotentiometer according to the invention and depicted in FIG. 1, thesection being taken as indicated by directors 3--3 in FIG. 2, andsubstantially at right angles to the section of the latter figure;

FIG. 4 is a transverse sectional view, the section being taken asindicated by directors 4-4 in FIG. 2, showing the presently preferredarrangement of the actuator and driving hub, first and second planetwheels, and the circular track or path on the interior surface or wallof the potentiometer housing means;

FIG. 5 is a transverse sectional view of portions of the exemplarypotentiometer, the section being taken as indicated by the directors 5-5in FIG. 2, and showing in detail the geometrical arrangement oforientation and stop devices and showing the nature of the movablecontact device;

FIG. 6 is an isometric view of the base device of the exemplarypotentiometer, the base device comprising a substrate, resistive andconductive devices, and termination members in the form of wirelikepins;

FIG. 7 is a vertical section, in isometric, of the manually operableactuator of the potentiometer, and a ring seal that is employed to barentrance of undesired foreign material into the interior of thepotentiometer; and

FIG. 8 is an exploded pictorial representation of the combined planetcarrier and contact carrier of the illustrated potentiometer, and thedisplaced planet wheels, one of the latter being shown in section.

DETAILED DESCRIPTION OF THE INVENTION In the accompanying drawings towhich reference is herein made, the illustrative potentiometer (FIG. 1),according to the invention, is illustrated grossly enlarged for the wakeof clarity. The potentiometer depicted is actually about 5/l6 inchdiameter and about /4 inch high excluding terminal pins. Thus toadequately and clearly portray details, gross enlargement is necessary.The depicted structure and mechanical arrangement, while conformingsubstantially exactly to an eminently successful embodiment of theinvention, is exemplary only and the nature and scope of the inventionare as defined by the appended claims.

The illustrated potentiometer comprises a generally hollow cylindricalinverted cuplike housing 22, the bottom of which is open and the top ofwhich is provided with a circular aperture 22a, as shown in FIGS. 1, 2and 3. Rotatable in the circular aperture 220 is the uppertool-receiving stub 24a of a manually rotatable actuator 24. As shown inFIGS. 3 and 7, the actuator stub is provided with a driver-receivingdepression in the form of a slot 240 for reception of a torque-applyingrotary tool such as the blade of a screwdriver. The stub is ofcylindrical configuration and has applied thereto an O-ring seal 26 asindicated, for example, in FIG. 7. The apertured web of the housing 22is provided with an annular recess 22r against the walls of which recessthe O-ring seal engages, as indicated in 'FIG. 3. The actuator has anannular flange 24f which rotatably bears on the inner face of thetransverse web of the housing 22, and is retained in that attitude by aringlike housing insert 28 (FIGS. 2, 3 and 5), the upper generallyannular flat face of which bears in part against the lower faceof theflange. The insert 28 performs orientation functions, as will bepresently explained.

Protruding or extending downwardly from the lower face of flange 24f ofthe actuator, and preferably formed as integral portions of theactuator, are a driving hub 24h and a rotary gudgeon 24g, both coaxialwith the potentiometer axis and both of cylindrical form and arranged asindicated in FIGS. 3 and 7. The hub 24h serves as a frictional drivingmember presently more fully explained, and gudgeon 24g serves as a guideor pivot about the axis of which a rotatable carrier 30 is arranged forrotation. The axis about which the hub, gudgeon and stub of actuator 24are rotatable is for convenience defined as the axis of thepotentiometer.

The carrier 30 is of circular plan form, as indicated in FIG. 4, androtates in free bearing relationship, within presently described angularstop-defined limits, inside an upper inner cylindrical wall surface 28b(FIG. 3) of the fixed housing insert 28. As indicated in FIG. 8, carrier30 is provided with a central longitudinally ribbed or fluted bore 30bthat is dimensioned for reception of gudgeon 24g of the actuator 24, andis provided with a shallow transverse recess 30r of dumbbell shape foraccommodation of hub 24h of the actuator and the disc portions of a setof substantially identical frictional planet wheels 32. The relativedispositions of the carrier, hub, gudgeon and planet wheels are asindicated in FIG. 2.

As is further indicated in FIG. 8, the carrier 30 is formed or providedwith a set (two, as shown) of radially extended slots 30:; centrallydisposed in respective outer enlargements of the shallow recess 30r. Theslots are formed and dimensioned to accommodate, with clearance for someradial movement as well as for rotation, the downwardly extending hubsor axles 32p of the planet wheels 32. The recess 30r is dimensioned, asindicated in FIGS. 2 and 4, so as to form, with the overlying flange ofactuator 24, a set of interconnected cells in which the respectiveplanet wheels are confined with capacity for easy rotation about theirrespective axes and for orbital motion with the rotary carrier.

In assembling the parts thus far described, the O-ring seal is fittedonto stub 24s and the actuator is lowered, topside down, into theinverted housing 22. The orienting housing insert 28 is then secured inplace against an ofiset or shelf formed on the interior of housing 22,as shown, adhesive means or pressfitting or the like being preferred forretaining the insert in fixed position. The insert is formed withunequally spaced longitudinal slots such as 28n (FIG. 4) whichaccommodate respective complementary inwardly extending longitudinalkeys such as 22k formed along the interior wall of housing 22. Theunequally spaced keys serve to facilitate and insure correct orientationduring assembly of the parts and proper positioning of a fixed stopmeans. Following installation of the insert 28, the assembly is invertedto upright position, the planet wheels are placed in position in therecess 30r of the carrier with their axles in respective ones of slots30c and the subassembly thus formed moved into position in the housing,care being taken that projecting rotary stop 30s (FIG. 8) thereon isdisplaced out of line with a stationary or fixed stop 28s (FIG. 5)formed on the interior of insert 28. Thus the rims of the planet wheelsare brought into compressional contact with a circular friction pathconveniently provided by the previously mentioned surface 28b on theinterior of the housing insert. Thereafter a base device 34, presentlydescribed, is rotationally oriented relative to the housing and ispressed into place with outer edge portions of its upper flat faceabutting the lower annular face 28f (FIG. 1) of insert 28, and the basedevice is sealed in place with potting compound or other sealant meanswhich in the interest of clarity of illustration has been omitted fromthe drawings.

The carrier 30 is a dual-purpose member or device of the potentiometermachinery, serving as a carrier and rotator for an electrical contactdevices 36 (FIG. 5) affixed to the lower face of the carrier, and as asupport and guide for the planetwheel portion of the "speed-reducing"driving means of the potentiometer. The contact device 36 is preferablyformed from an integral thin sheet of precious (noncorroding) metal,with a folded base portion 36b (FIG. 3) pressed into and corn pressivelyengaging the walls of a slot or recess 30c formed in the base of carrier30, and with first and second sets of resilient contact fingers 36m and36n (FIG. 5) extending angularly away from the lower face of the carrierbut adapted to be stressed into a shallow extension 30f of the recess30e in the bottom face of the carrier, as indicated in FIGS. 3 and 5.The contact device, which may herein be termed the contact in theinterest of brevity, may if desired be additionally secured in place inthe recess in the carrier by filling the base-receiving recess 30e withcement or potting compound (not shown in the interest of clarity ofillustration).

The base device 34 (FIG. 6) is formed with key slots such as 34n thatare complementary to and dimensioned and disposed to receive respectiveones of the keys 22k of the housing 22, whereby proper angularrelationship or orientation between parts is assured. The base devicecomprises an insulation substrate 34a that preferably is of alumina orthe like, and on the flat upper face of which substrate are formed firstand second conductive termination films 34c and 34d, a. centralconductive film 34c, and an arcuate resistive film or element 34r. Theresistance element 34r is preferably of cen-net material, fired inplace, but may be of other composition. The conductive films are formedfrom applied conductive metal paint, in known manner. The base devicefurther comprises terminal conductors that are in the form of wirelikepins, 34x, 34y and 34z (FIG. 6), that are each secured in a respectiveone of through-holes formed in the substrate, by solder or conductivecement for example, as indicated at 34s in H0. 2, with their upper endsin conductive contact with respective ones of the conductive films. Thuspin 34x is electrically connected to one end of element 34r by way offilm 34c, pin 34y is similarly electrically connected to the other endof the element 34r, and pin 34z is connected to the central conductivefilm 34c which is herein termed the return conductor.

When the base device is moved into position in the housing, the element34r is brought into contact with and compresses contact fingers 36m, andreturn conductor 34c similarly contacts and compresses contact fingers36", and thus the variable electrical circuit of the potentiometer isestablished. Rotation of the carrier moves contact fingers 36m along anarcuate brushing or contact path extending between termination films 34cand 34d, the extent of possible rotary movement being restricted byarrestment of stop 30s on the carrier by the stop 28: formed on theinner face of housing insert 28 and positioned in the circular path inwhich the rotary stop 30s moves. The dimensioning and dispositions ofthe stops, contact device and element 34r are such that rotation of thecarrier from either extreme or limit of its prescribed extent ofrotational movement causes brushing of element 34r by contact fingers36m from one electrical end of the element to the other, the totalarcuate traverse being less than 360.

Rotation of the carrier and the contact device is effected by rotationof the actuator 24. When the latter is rotated, the frictional surfaceof hub 24h rotates and, due to frictional engagement of rim portions ofeach of the set of planet wheels with both the hub 24/1 and the circularinterior friction surface 28b of the housing insert, the planet wheelsrotate about their respective axes and travel along the circularfriction path provided by surface 28b on which they bear or press. Asthey so travel, their axles 32p force the carrier to rotate about theresistance element. As is indicated in FIG. 4, the planet wheels haveresilient deformable frictional rim portions, and are dimensioned to beslightly diametrically compressed when in operable position in thepotentiometer, whereby the noted driving action occurs. The planetwheels may have rims of, or be entirely composed of, resilientfrictional material such as resilient synthetic rubber or resin polymer,and, depending upon the 'material used for driving hub 2411, the lattermay be smooth or rough, It is thus evident that, due to the differencebetween the diameter (or circumference) of driving hub 24h and thediameter (or circumferential length) of the clrcular frictional path onsurface 28b, several rotations or turns of the actuator hub (and of theactuator) are necessary to cause the planet wheels to travel along thepermitted extent of the circular path 28b formed on the interior of thehousing. The rotary motion is effected without the necessity of gears.ln the illustrated potentiometer, the planet wheels have a maximumdiameter of approximately five sixty-fourths of an inch and the actuatorhub is of the order of one thirty-seconds of an inch, whereby it isevident that gear teeth would be impractical in such miniaturesingle-tum adjustment potentiometers. When an operator overdrives theactuator 24, as is extremely easy due to the very small size of theinstrument, harmless slipping occurs between the driving hub 24h and theplanet wheels as soon as the stops 28s-30s arrest rotation of thecarrier, and thus no damage to the parts occurs. As is evident, even ifvery strong and expensive fine gauge gears were employed, stripping andruinous damage could easily occur. The described arrangement andconstruction, in which the housing, actuator, planet wheels and carrierare easily produced from inexpensive synthetic polymer material bymolding techniques, avoids any possibility of overdriving damage whileconcurrently affording the much desired speed-reduction effeet betweenthe manually operated actuator and the movable contact and aneconomically feasible potentiometer. While the housing 22 has beenillustrated as being of circular form having standoff feet 22f, it isevident that the exterior plan form of the housing may be octagonal, orsquare, or of other geometrical form, it being essential only that acircular interior track (or an equivalent pair of arcuate tracks) beprovided for travel of the planet wheels, and an axis of rotation forrotary parts such as the actuator and the carrier.

Having disclosed and explained in detail the presently preferredembodiment of the invention, it is evident that the mentioned objectshave been attained, and 1 claim:

1. A miniature single-tum adjustment potentiometer comprising, incombination:

first means including housing means, providing a smooth circularfriction path on the interior of said housing means;

second means, including a manually-rotatable actuator supported by saidfirst means and having a portion exposed for application of drivingtorque thereto, and a second portion comprising a rotary frictiondriving surface;

third means, including base means, supported by said first means in alower portion of said housing means, said third means including anarcuate resistance element and return conductor means;

fourth means, including a rotatable carrier arranged for rotation insaid housing means interposed between said rotatable actuator and saidbase means, said fourth means including an electrical contact movable bysaid carrier along an arcuate path of contact with said resistanceelement, said contact brushing on said return conductor means;

and fifth means, including a set of rotatable friction wheels carried bysaid carrier and pivotally supported thereon each with a rim surfacepressing radially in operative frictional engagement with said frictionpath and pressing radially in operative frictional engagement with saidfriction driving surface, said rotatable carrier and said rotatablefriction wheels comprising cooperating means permitting radialadjustment movement of said wheels whereby radial forces exerted on saidwheels are equalized,

whereby incident to rotation of said actuator said friction wheels arerotated by said friction driving surface and travel along said circularfriction path and rotate said carrier to move said contact along saidarcuate path of contact at a rotational rate less than that of saidactuator.

2. A potentiometer according to claim 1, in which said first meansincludes a fixed stop means and in which said fourth means includes amovable stop means disposed and arranged to be arrested by said fixedstop means at predetermined extremes of the movement of said contactalong said arcuate path of contact. whereby said contact is preventedfrom moving of? either extremity of said arcuate path of contact of saidresistance element.

3. In a miniature single-turn rotary adjustment potentiometer of thetype comprising housing means, an arcuate resistance element, a returnconductor, a rotary contact brushing on the resistance element andconnected with the return conductor, and a manually rotatable actuatormeans to receive applied torque for effecting movement of the contactalong the resistance element; mechanical means interposed between therotatable actuator and the contact whereby more than one revolution ofthe actuator is required for movement of the contact throughout thearcuate extent of the resistance element, said mechanical meanscomprising a carrier rotatably supported in said housing means forrotation about an axis and carrying the said contact, a set of frictionplanet wheels carried by the carrier, a smooth circular driving frictionsurface on said actuator means in frictional driving relationship withsaid planet wheels, and said housing means providing smooth arcuatepaths coaxial with said axis for travel therealong by respective ones ofsaid planet wheels and in frictional contact with respective ones ofsaid wheels, said carrier and said friction wheels comprisingcooperating means permitting free radial adjustment of said wheels toequalize radial forces on said wheels, whereby incident to rotation ofsaid driving friction surface said planet wheels are rotated and travelalong respective ones of said arcuate paths and along orbital pathsrelative to said axis to thereby rotate said carrier and move saidcontact along said resistance element, and whereby a plurality ofrevolutions of said actuator means are required to move said contactfrom either end of said arcuate resistance element to the other endthereof to permit very fine adjustment of said contact.

4. A potentiometer according to claim 3, in which said housing meanscomprises a circular aperture in which said actuator is rotatable anddefines an axis, and in which said rotatable carrier and said actuatorcomprise cooperating bearing means coaxial with said axis and comprise arotatable pivot on one of said actuator and said carrier and apivot-receiving bore in the other of said actuator and said carrier,whereby said carrier is constrained to rotation about said axis and saidplanet wheels are constrained to circular orbital paths having said axisas a center.

5. A potentiometer according to claim 3, in which said housing means andsaid carrier comprise fixed and movable stop means, respectively, sopositioned as to restrict said carrier and the contact carried therebyto rotational movements of less than one complete revolution, saiddriving friction surface and said frictional contact of said path withsaid wheels permitting slipping of frictional surfaces in saidmechanical means incident to continued rotation of said driving surfacefollowing engagement of said fixed stop means by said movable stopmeans, whereby damage to said mechanical means and said contact isavoided.

6. A potentiometer according to claim 3, in which said carrier comprisesslot-shaped axle-receiving bearing means and said planet wheels eachcomprise a stub axle rotatably received in a respective one of saidbearing means, whereby said planet wheels may assume positions in whichopposed forces exerted on their rims by said driving friction surfaceand said arcuate paths are equalized to provide freedom from binding ofsaid planet wheels.

7. A potentiometer according to claim 3, in which said carrier isprovided with recesses in its upper face, in which recesses said planetwheels are nested for rotation, and in which potentiometer saidrotatable actuator means comprises a flange overlying said planet wheelsand confining said planet wheels to said recesses, whereby saidmechanical means is made simple and inexpensive.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 614,703 Dated October 19, 1971 Inventor(s) Ronald L. Froebe It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 10, "contacting" should read contact. Column 1, line 54,"will" should read while-. Column 2, line 61, insert --board after"primary". Column 3, line 4, insert aafter "are". Column 3, line 22,insert opposed-- after "second". Column 3, line 32, "conductive" shouldread conductor-. Column 3, line 47, "wake" should read sake-. Column 3,line 61, "24a" should read --24s. Column 4, line 72, "devices" shouldread device--. Column 5, line 63, insert potentiometer axis, carryingthe contact along the after "rotate about the".

Signed and sealed this 25th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER.JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM 304050 uscoMM-Dc 60376-P69 a U S. GOVIRNHENY FRINYINGOFFICE 1969 0-366-33

1. A miniature single-turn adjustment potentiometer comprising, incombination: first means including housing means, providing a smoothcircular friction path on the interior of said housing means; secondmeans, including a manually-rotatable actuator supported by said firstmeans and having a portion exposed for application of driving torquethereto, and a second portion comprising a rotary friction drivingsurface; third means, including base means, supported by said firstmeans in a lower portion of said housing means, said third meansincluding an arcuate resistance element and return conductor means;fourth means, including a rotatable carrier arranged for rotation insaid housing means interposed between said rotatable actuator and saidbase means, said fourth means including an electrical contact movable bysaid carrier along an arcuate path of contact with said resistanceelement, said contact brushing on said return conductor means; and fifthmeans, including a set of rotatable friction wheels carried by saidcarrier and pivotally supported thereon each with a rim surface pressingradially in operative frictional engagement with said friction path andpressing radially in operative frictional engagement with said frictiondriving surface, said rotatable carrier and said rotatable frictionwheels comprising cooperating means permitting radial adjustmentmovement of said wheels whereby radial forces exerted on said wheels areequalized, whereby incident to rotation of said actuator said frictionwheels are rotated by said friction driving surface and travel alongsaid circular friction path and rotate said carrier to move said contactalong said arcuate path of contact at a rotational rate less than thatof said actuator.
 2. A potentiometer according to claim 1, in which saidfirst means includes a fixed stop means and in which said fourth meansincludes a movable stop means disposed and arranged to be arrested bysaid fixed stop means at predetermined extremes of the movement of saidcontact along said arcuate path of contact, whereby said contact isprevented from moving off either extremity of said arcuate path ofcontact of said resistance element.
 3. In a miniature single-turn rotaryadjustment potentiometer of the type comprising housing means, anarcuate resistance element, a return conductor, a rotary contactbrushing on the resistance element and connected with the returnconductor, and a manually rotatable actuator means to receive appliedtorque for effecting movement of the contact along the resistanceelement; mechanical means interposed between the rotatable actuator andthe contact whereby more than one revolution of the actuator is requiredfor movement of the contact throughout the arcuate extent of theresistance element, said mechanical means comprising a carrier rotatablysupported in said housing means for rotation about an axis and carryingthe said contact, a set of friction planet wheels carried by thecarrier, a smooth circular driving friction surface on said actuatormeans in frictional driving relationship with said planet wheels, andsaid housing means providing smooth arcuate paths coaxial with said axisfor travel therealong by respective ones of said planet wheels and infrictional contact with respective ones of said wheels, said carrier andsaid friction wheels comprising cooperating means permitting free radialadjustment of said wheels to equalize radial forces on said wheels,whereby incident to rotation of said driving friction surface saidplanet wheels are rotated and travel along respective ones of saidarcuate paths and along orbital paths relative to said axis to therebyrotate said carrier and move said contact along said resistance element,and whereby a plurality of revolutions of said actuator means arerequired to move said contact from either end of said arcuate resistanceelement to the other end thereof to permit very fine adjustment of saidcontact.
 4. A potentiometer according to claim 3, in which said housingmeans comprises a circular aperture in which said actuator is rotatableand defines an axis, and in which said rotatable carrier and saidactuator comprise cooperating bearing means coaxial with said axis andcomprise a rotatable pivot on one of said actuator and said carrier anda pivot-receiving bore in the other of said actuator and said carrier,whereby said carrier is constrained to rotation about said axis and saidplanet wheels are constrained to circular orbital paths having said axisas a center.
 5. A potentiometer according to claim 3, in which saidhousing means and said carrier comprise fixed and movable stop means,respectively, so positioned as to restrict said carrier and the contactcarried thereby to rotational movements of less than one completerevolution, said driving friction surface and said frictional contact ofsaid path with said wheels permitting slipping of frictional surfaces insaid mechanical means incident to continued rotation of said drivingsurface following engagement of said fixed stop means by said movablestop means, whereby damage to said mechanical means and said contact isavoided.
 6. A potentiometer according to claim 3, in which said carriercomprises slot-shaped axle-receiving bearing means and said planetwheels each comprise a stub axle rotatably received in a respective oneof said bearing means, whereby said planet wheels may assume positionsin which opposed forces exerted on their rims by said driving frictionsurface and said arcuate paths are equalized to provide freedom frombinding of said planet wheels.
 7. A potentiometer according to claim 3,in which said carrier is provided with recesses in its upper face, inwhich recesses said planet wheels are nested for rotation, and in whichpotentiometer said rotatable actuator means comprises a flange overlyingsaid planet wheels and confining said planet wheels to said recesses,whereby said mechanical means is made simple and inexpensive.